The present invention relates in general to sewing machine controls, and in particular to a new and useful device for controlling the drive of a stepping motor which is provided to adjust the lateral stitch bight and/or the feed length of a sewing machine which is connected to the stepping motor for varying the frequency of the stepping motor as a function of the speed of the sewing machine.
The control device for a stepping motor in a sewing machine of the prior art has the drawback that due to the strong current increase in the windings of the motor and, consequently, the very rapid acceleration and deceleration both of the motor and the driven external masses during the jerky execution of the rotary steps, a very big noise is produced. In addition, resonances appear at certain frequency steps of the stepping motor and oscillations are produced about the respective dwell position, further raising the noise level.